Methods for forming and releasing microelectromechanical structures

ABSTRACT

A method for making a spatial light modulator is disclosed, that comprises forming an array of micromirrors each having a hinge and a micromirror plate held via the hinge on a substrate, the micromirror plate being disposed in a plane separate from the hinge and having a hinge made of a transition metal nitride, followed by releasing the micromirrors in a spontaneous gas phase chemical etchant. Also disclosed is a projection system that comprises such a spatial light modulator, as well as a light source, condensing optics, wherein light from the light source is focused onto the array of micromirrors, projection optics for projecting light selectively reflected from the array of micromirrors onto a target, and a controller for selectively actuating the micromirrors in the array.

This application is a continuation-in-part of a) U.S. patent applicationSer. No. 10/155,744 to Huibers et al, filed May 24, 2002, now U.S. Pat.No. 6,741,383 which is a continuation-in-part of U.S. patent applicationSer. No. 09/637,479 to Huibers et al, filed Aug. 11, 2000 now U.S. Pat.No. 6,396,619; b) U.S. patent application Ser. No. 10/005,308 to Patelet al, filed Dec. 3, 2001, which claims priority to U.S. provisionalapplication 60/254,043 to Patel et al., filed Dec. 7, 2000; c) U.S.patent application Ser. No. 10/343,307 to Huibers filed Jan. 29, 2003,which is a U.S. national phase application of PCT/US01/24332 filed Aug.3, 2001, which claims priority to U.S. provisional application60/229,246 to Ilkov et al. filed Aug. 30, 2000; d) U.S. patentapplication Ser. No. 10/176,478 to Reid, filed Jun. 21, 2002, whichclaims priority to U.S. provisional application 60/300,533, filed Jun.23, 2001; e) U.S. patent application Ser. No. 09/954,864 to Patel et al,filed Sep. 17, 2001, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/427,841 filed Oct. 26, 1999 (now U.S. Pat. No.6,290,864) and U.S. patent application Ser. No. 09/649,569 filed Aug.28, 2000; f) U.S. patent application Ser. No. 10/346,506 to Huibers etal, filed Jan. 15, 2003, which claims priority to U.S. provisionalapplication 60/349,798, filed Jan. 16, 2002; and g) U.S. patentapplication Ser. No. 10/365,951 to Doan et al, filed Feb. 12, 2003. Eachof the above applications are incorporated herein by reference in theirentirety.

TECHNICAL FIELD OF THE INVENTION

The present invention is related generally to spatial light modulators,and, more particularly, to fabrications of spatial light modulators withhinge structures made of particular materials that withstand spontaneousgas phase chemical etchants.

BACKGROUND OF THE INVENTION

Spatial light modulators (SLMs) are transducers that modulate anincident beam of light in a spatial pattern in response to an optical orelectrical input. The incident light beam may be modulated in phase,intensity, polarization, or direction. This modulation may beaccomplished through the use of a variety of materials exhibitingmagneto-optic, electro-optic, or elastic properties. SLMs have manyapplications, including optical information processing, display systems,and electrostatic printing.

Spatial light modulators in projection displays that have micromirrorarrays generally have plate portions for reflecting light and hingeportions for allowing movement of the plate portions, such as inresponse to an electrostatic attraction from an adjacent electrode. Theplate portions can be rotated between ON and OFF positions, where lightis directed through projection optics from ON micromirrors onto atarget. The micromirrors can be operated in analog mode or in digitalpulse width modulation mode in order to obtain gray scale at eachmicromirror location. A color sequencing device, such as a prism orcolor wheel, can be used to create a color image—or dedicated spatiallight modulators for individual colors can be used.

SUMMARY OF THE INVENTION

In one embodiment of the invention, a method for making a MEMS device,comprises: depositing a sacrificial material on a substrate; forming anarray of MEMS elements comprised of plates and hinges, wherein thehinges of the MEMS elements comprise an early transition metal (groups3b-7b of the periodic table) nitride; and releasing the MEMS elements byremoving the sacrificial material in a spontaneous gas phase chemicaletchant selected from interhalogens and noble gas halides, wherein theearly transition metal nitride is exposed to the etchant during removalof the sacrificial material but remains after the MEMS elements arereleased.

In another embodiment of the invention, a method for making amicromirror array for a projection display, comprises depositing asacrificial material on a substrate; forming an array of micromirrorscomprised of mirror plates and hinges, wherein the hinges of themicromirrors comprise an early transition metal (groups 3-7 of theperiodic table) nitride; and releasing the micromirrors by removing thesacrificial material in a spontaneous gas phase chemical etchantselected from interhalogens and noble gas halides, wherein the earlytransition metal nitride is exposed to the etchant during removal of thesacrificial material but remains after the micromirrors are released.

BRIEF DESCRIPTION OF DRAWINGS

While the appended claims set forth the features of the presentinvention with particularity, the invention, together with its objectsand advantages, may be best understood from the following detaileddescription taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 diagrammatically illustrates an exemplary display systememploying a spatial light modulator;

FIG. 2 is a top-view of the spatial light modulator used in the displaysystem of FIG. 1;

FIG. 3A is a back-view of a set of micromirrors according to anembodiment of the invention;

FIG. 3B illustrates a hinge-structure of the micromirrors of FIG. 3A;

FIG. 3C is a back-view of a set of micromirrors according to anotherembodiment of the invention;

FIG. 3D shows a hinge-structure of the micromirrors of FIG. 3C;

FIG. 3E illustrates therein a hinge-structure according to yet anotherembodiment of the invention;

FIG. 3F illustrates therein a hinge-structure according to yet anotherembodiment of the invention;

FIG. 3G illustrates therein a hinge-structure according to anotherembodiment of the invention;

FIG. 4A is a cross-sectional view of the micromirror device in an “OFF”state;

FIG. 4B is a cross-sectional view of the micromirror device in another“OFF” state;

FIG. 4C is a cross-sectional view of the micromirror device in an “ON”state;

FIG. 4D is a cross-sectional view of the micromirror device in yetanother “OFF” state, wherein the hinge-structure has two sets of mirrorstops;

FIG. 4E is a cross-sectional view of another embodiment of themicromirror device with the mirror in the “ON” state;

FIG. 5A is a cross-sectional view of a micromirror device having ahinge-support that curves at a natural resting state;

FIG. 5B is a cross-sectional view of an exemplary hinge-support beforereleasing according to an embodiment of the invention;

FIG. 5C is a cross-sectional view of the hinge-support of FIG. 5B afterreleasing;

FIG. 6A to FIG. 6H are cross-sectional views of structures illustratinga method for forming a micromirror device according an embodiment of theinvention;

FIG. 7A to FIG. 7B are cross-sectional views of structures illustratinganother method for forming a micromirror device according to anotherembodiment of the invention; and

FIG. 8 presents a cross-sectional view of a micromirror device afterreleasing by removing the sacrificial layers.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Methods

Processes for micro-fabricating a MEMS device such as a movablemicromirror and mirror array are disclosed in U.S. Pat. Nos. 5,835,256and 6,046,840 both to Huibers, the subject matter of each beingincorporated herein by reference. A similar process for forming MEMSmovable elements (e.g. mirrors) on a wafer substrate (e.g. a lighttransmissive substrate or a substrate comprising CMOS or othercircuitry) is illustrated in the present application. By “lighttransmissive”, it is meant that the material will be transmissive tolight at least in operation of the device (The material couldtemporarily have a light blocking layer on it to improve the ability tohandle the substrate during manufacture, or a partial light blockinglayer for decreasing light scatter during use. Regardless, a portion ofthe substrate, for visible light applications, is preferablytransmissive to visible light during use so that light can pass into thedevice, be reflected by the mirrors, and pass back out of the device. Ofcourse, not all embodiments will use a light transmissive substrate). By“wafer” it is meant any substrate on which multiple micromirrors ormicrostructure arrays are to be formed and which allows for beingdivided into dies, each die having one or more micromirrors thereon.Though not in every situation, often each die is one device or productto be packaged and sold separately. Forming multiple “products” or dieson a larger substrate or wafer allows for lower and faster manufacturingcosts as compared to forming each die separately. Of course the waferscan be any size or shape, though it is preferred that the wafers be theconventional round or substantially round wafers (e.g. 4″, 6″ or 12″ indiameter) so as to allow for manufacture in a standard foundry.

The present invention provides a spatial light modulator that has ahigher resolution, an increased fill factor, and an increased contrastratio in displaying an image. The spatial light modulator may beoperated in the absence of polarized light. Moreover, the spatial lightmodulator has improved electro-mechanical performance and robustnesswith respect to manufacturing.

The spatial light modulator of the present invention has a variety ofapplications (e.g. maskless lithography, atomic spectroscopy, masklessfabrication of micromirror arrays, signal processing, microscopy etc),one of which is in display systems. A typical display system employing aspatial light modulator is illustrated in FIG. 1. In its very basicconfiguration, the display system comprises light source 120, opticaldevices (e.g. light pipe 150, collection optics 160 and projectionoptics 190), display target 210 and spatial light modulator 200. Lightsource 120 (e.g. an arc lamp) directs light through the lightintegrator/pipe 150 and collection optics 160 and onto spatial lightmodulator 200. The micromirrors of the spatial light modulator 200 areselectively actuated by a controller (e.g. as disclosed in U.S. Pat. No.6,388,661 issued May 14, 2002 incorporated herein by reference) so as toreflect—when in their “ON” position—the incident light into projectionoptics 190, resulting in an image on display target 210 (screen, aviewer's eyes, a photosensitive material, etc.). Of course, more complexoptical systems are often used—the display system of FIG. 1 being asimplification of a typical projection display optical system.

The spatial light modulator, in general, comprises an array of thousandsor millions of micromirrors. FIG. 2 illustrates a portion of anexemplary micromirror array. Referring to FIG. 2, a top-view of aportion of an exemplary spatial light modulator 200 looking throughglass is illustrated therein. As shown, the spatial light modulatorcomprises micromirror array 201 that is formed on a substrate 202, suchas glass that is visible light transmissive. Alternatively, substrate202 is a typical semiconductor wafer that has formed thereon an array ofelectrodes and circuitry (not shown in FIG. 2) for electrostaticallycontrolling motions of the micromirrors. Micromirror array 201 comprisesa plurality of micromirror devices, such as micromirror device 215. Andeach micromirror device further comprises a reflective micromirrorplate, such as micromirror plate 210 for reflecting the incident light.In operation, each individual micromirror can be deflected as desiredunder the control of one or more electrodes and circuitry, thereby thespatial modulation of the incident light traveling through substrate 202(in this case, the substrate is a glass) and incident on the surfaces ofthe micromirrors can be achieved. To facilitate the micromirror platerotating above the substrate (or below, depending upon the point ofview) for reflecting the incident light, a hinge-structure is necessaryto hold the micromirror plate above the substrate and provide a meansfor rotation of the micromirror plate.

Referring to FIG. 3A, a back-view of the micromirror array (e.g. 201)shown in FIG. 2 is illustrated therein. Each micromirror plate (e.g.micromirror 210) is attached to a hinge-structure (e.g. hinge structure230) such that the micromirror plate can pivot along the hinge structureabove the substrate (e.g. substrate 202 in FIG. 2). In order to improvethe quality of displayed images, the hinge structure is preferablyformed under the micromirror plates as shown. Specifically, the hingestructure and the surface for reflecting the incident light are on theopposite sides of the micromirror plate.

According to an embodiment of the invention, the micromirror plate isattached to the hinge structure such that the micromirror plate canpivot along an axis that is parallel to but offset from a diagonal ofthe micromirror plate (when viewed as both a cross section and as a topview). For example, micromirror plate 210 has a well defined geometricaldiagonal 211. However, the rotation axis of the micromirror plate isalong direction 213 that is parallel to but offset from diagonal 211.Such a rotation axis can be achieved by attaching the hinge structure tothe mirror plate at a point not along the mirror plate diagonal 211. Thepoint of attachment can be at least 0.5 um, at least 1 um, or at least 2um away from the diagonal 211. In one embodiment, the point ofattachment is from 1/40 to ⅓ the length of the diagonal away fromdiagonal 211, or from 1/20 to ¼ if desired—although any desired distanceaway from the diagonal is possible if so desired in the presentinvention. In the present invention, the micromirror preferably has asubstantially four-sided shape. Whether the micromirror is a rectangle,square, rhombus or trapezoid, even if the corners are rounded or“clipped” or if an aperture or protrusion is located on one or more ofthe sides of the micromirror, it is still possible to conceptuallyconnect the four major sides of the micromirror shape and take adiagonal across the middle of the micromirror. In this way, a centerdiagonal can be defined even if the micromirror plate is substantiallybut not perfectly a rhombus, trapezoid, rectangle, square, etc. However,the rotation axis of the micromirror plate is not along the centerdiagonal but is along direction 213 that is parallel to but offset fromdiagonal 211 in FIG. 3A. By “parallel to but offset from the diagonal”,it is meant that the axis of rotation can be exactly parallel to orsubstantially parallel to (±19 degrees) the diagonal of the micromirror.This type of design benefits the performance of the micromirror devicein a number of ways. One advantage of this asymmetric offset arrangementis that the micromirror plate can rotate at a larger angle than therotation angle that can be achieved in a symmetrical arrangement (with amirror plate—substrate gap being the same). The length of the diagonalof the mirror plate is preferably 25 microns or less.

In order to hold the micromirror plate and meanwhile, provide amechanism for rotation of the micromirror plate above the substrate,each hinge structure, such as hinge structure 230, further compriseshinge-support 250 and hinge 240, as shown in FIG. 3B. Hinge 240 isattached to the micromirror plate via contact 257. Hinge support 250further comprises two posts 251. By “hinge” is meant the layer or stackof layers that defines that portion of the device that flexes to allowmovement of the device (described in detail below). To improve theperformance of the micromirror plate, further fine structures are alsoprovided thereon. Specifically, two mirror stops 255 are formed on anedge of hinge support 250 for stopping the rotation of the micromirrorplate when the micromirror plate achieves a certain angle. Thegeometrical arrangement, such as the length and the position of themirror stop from the hinge-plate, along with the distance between themicromirror plate and the hinge determines the maximum rotation anglethat the micromirror can achieve before contact. By properly setting themirror stops for all micromirror plates in the micromirror array, amaximum rotation angle for all micromirrors can be uniformly defined.This uniformly defined rotation angle can then be defined as an “ON”state for all micromirrors in operation. In this case, all micromirrorsin the spatial light modulator rotate to the uniformly defined angle inthe “ON” state in an operation. The incident light can thus be uniformlyreflected towards one desired direction for display. Obviously, thissignificantly improves the quality of the displayed image. Thoughpreferred, the number of the mirror stops can be of any desired number(one or more) or need not be provided at all. And each mirror stop canbe of any desired shape, though preferably one that minimizes the amountof contact between the mirror stop and the micromirror plate.

In the embodiment of the invention, the two posts are formed on thesubstrate. Hinge-support 250 is supported by the two posts above thesubstrate. The hinge (e.g. hinge 240) is affixed to the hinge-supportand attached to the micromirror plate via the contact (e.g. contact255). In this configuration, the micromirror plate can pivot along thehinge above the substrate.

The hinge structure can take other suitable forms as desired. FIG. 3Cillustrates another hinge structure design according to anotherembodiment of the invention. Similar to that of FIG. 3A, hinge structure260 is formed on the substrate for supporting micromirror plate 210 andprovides a rotation axis 214 for the micromirror plate. Rotation axis214 is parallel to, but offset from a diagonal of micromirror plate 212.Similar to hinge-support 250 in FIG. 3B, hinge-support 263 in FIG. 3Dalso has a plurality of mirror stops formed thereon for stopping therotation of the micromirror plate when the micromirror plate achieves acertain angle. The geometrical arrangement, such as the length and theposition on the hinge-support, along with the distance between themicromirror plate and the hinge determines the maximum rotation anglethat the micromirror can achieve before contact. Though preferred, thenumber of the mirror stops can be of any desired number. And each mirrorstop can be of any desired shape.

The hinge structure can also take other suitable forms. For example,hinge support 261 can be formed along the edges of one part of themicromirror plate such that the hinge-support passes through a post ofadjacent micromirror device, as shown in FIG. 3E In this case, thehinge-support of all micromirror devices form a continuous hinge-supportframe for all micromirror plates. This allows 2-dimensional electricalconnection of the micromirrors in the array.

Alternatively, the posts of each hinge structure are not required to beformed along the diagonal of the micromirror plate. Referring to FIG.3F, two posts 251 of the hinge structure are formed along the edges ofthe micromirror plate instead of at the corners of the micromirrorplate. In addition, the hinge is not required to be placed such that thehinge and the two arms intersected with the hinge form an isoscelestriangle, as shown in the figure. Instead, as shown in FIG. 3G, thehinge may be placed such that it is substantially parallel but forms asmall angle (±19 degrees) with the hinge position in FIG. 3F.

In operation, the micromirror plate rotates along the hinge that isparallel to but offset from a diagonal of the micromirror plate. Basedon rotation angles, “ON” and “OFF” states are defined. At the “ON”state, the micromirror plate is rotated to a predefined angle such thatthe incident light can be reflected into a direction for view, forexample, into a set of pre-arranged optic devices for directing lighttowards a target. In the “OFF” state, the micromirror plate stays flator at another angle such that the incident light will be reflected awayfrom the display target. FIG. 4A through FIG. 4D illustratecross-sectional views of a micromirror device in operation.

Referring to FIG. 4A, an “OFF” state is define as micromirror plate 210at its natural resting state that is parallel to glass substrate 280.Hinge support 263 is formed on the substrate for supporting themicromirror plate. The hinge (e.g. hinge 240 in FIG. 3B) is affixed tohinge-support 263 and attached to micromirror plate 210 via shallow viacontact 241 (hereafter “contact”) for providing a rotational axis forthe micromirror plate. In this “OFF” state, the incident light travelsthrough the glass substrate, shines on one surface of the micromirrorplate at a particular incident angle and is reflected away from thetarget by the micromirror plate. The rotation of the micromirror platecan be electrostatically controlled by electrode 282 and a circuitry(not shown) that is connected to the electrode. In an embodiment of theinvention, the electrode and circuitry are formed in wafer 281, whichcan be a typical silicon wafer. In order to efficiently control therotation of the micromirror plate, wafer 281 is placed proximate to themicromirror plate such that electrostatic fields can be establishedbetween micromirrors and associated electrodes. Alternatively, more thanone electrode can be used for controlling the rotation of themicromirror plate. Specifically, electrode 283 (and circuitry connectedto the electrode, which is not shown) can be formed and placedunderneath the other portion of the micromirror plate for controllingthe micromirror plate in an “OFF” state, as shown in FIG. 4B. In anotherembodiment of the invention, the electrodes, the circuitry and themicromirrors can be formed on the same substrate, such as substrate 280.In this case, substrate 280 can be a standard silicon wafer. And theincident light shines the opposite surface of the micromirror plate. Toimprove the quality of the displayed image, especially the contrastratio, it is desired that the reflected light in the “OFF” state bereflected as much as possible away from the collection optics or target.To achieve this, another “OFF” state is defined as shown in FIG. 4B.Referring to FIG. 4B, micromirror plate 210 is rotated at an angle inthe “OFF” state. As an optional feature, the angle corresponding to this“OFF” state is defined such that one end of the micromirror platetouches and is stopped by the substrate when the micromirror plate isrotated to this angle. This definition ensures a uniform “OFF” state forall micromirror plates in the micromirror array. Of course, othermethods can also be employed in defining an “OFF” state angle. Forexample, by properly controlling the electric field applied between themicromirror plate and the electrode(s) and circuitry associated with themicromirror plate, desired angles “corresponding to the “OFF” state canbe achieved. In order to direct the reflected light into the target fordisplaying, the micromirror plate needs to be rotated to a certainangle, which is corresponds to an “ON” state. FIG. 4C illustrates across-sectional view of the micromirror device in an exemplary “ON”state according to an embodiment of the invention. In this “ON” state,the rotation of the micromirror plate is stopped by mirror stops 270. Byadjusting the configuration (e.g. length and the position on the hingestructure) of the mirror stops, the angle corresponding to the “ON”state can thus be adjusted, as long as the other end of the micromirrorplate is free to move. The presence of the mirror stops benefit auniform “ON” state for all micromirror plates in the spatial lightmodulator, thus, the quality of the displayed image is significantlyimproved. As an optional feature of the embodiment, the mirror stops canbe designed and formed such that the other end of the micromirror platetouches and is stopped by the substrate when the rotation of themicromirror plate touches and is stopped by the mirror stops, as shownin FIG. 4C. This dual-stopping mechanism further guarantees a uniformrotation angle corresponding to the “On” state for all micromirrorplates. As a further optional feature, another set of mirror stops forthe “OFF” state may also be provided in addition to the set of mirrorstops for the “ON” state, as shown in FIG. 4D.

Referring to FIG. 4D, a first set of mirror stops 270 is formed on thehinge structure for providing a uniform “ON” state for all micromirrorplates. And a second set of mirror stops 275 is further provided forensuring a uniform “OFF” state for all micromirror plates. The physicalproperties (e.g. length and position) of the second set of mirror stops275 determine the rotation position of the “OFF” state. Alternatively,the second set of mirror stops can be designed and formed such that theother end of the micromirror plate touches and is stopped by the glasssubstrate when the micromirror plate touches and is stopped by thesecond set of mirror stops.

In operation, the micromirror plate (e.g. 210 in FIG. 3C) rotates andreflects incident light via projection optics to a target. This type ofoperation mechanism calls for certain requirements on the optical,mechanical and electric properties of the micromirror plate, hingestructure and contact 255. In particular, the micromirror plate isdesired to comprise a material having high reflectivity to the light ofinterest, for example, a material of early transition metal, metal (e.g.aluminum) or metal alloy. In addition, it is desired that the materialof the micromirror plate also exhibits suitable mechanical properties(e.g. large strength and high elastic modulus etc.) for enhancing themechanical property of the micromirror plate. Furthermore, it is desiredthat the material of the micromirror plate is electrically conductivesuch that an electric voltage can be applied thereto.

The hinge-support (e.g. 260 in FIG. 3C) provides an axis by which themicromirror plate (e.g. micromirror plate 210) can rotate. Because thehinge-support may scatter incident light and the scattered light can bemingled with the reflected light, thereby, the contrast ration can bedegraded. In order to suppress this type of scattering, the hingestructure is preferably “hidden” beneath the micromirror plate. Forexample, the hinge structure is formed on a side of the micromirrorplate that is opposite to the side of the micromirror plate reflectingthe incident light. In accordance with the operation mechanism of themicromirror plate and the constructional design, it is desired that theposts comprise materials that are insusceptible to plastic deformation(e.g. fatigue, creep, dislocation motion) during the operation of thedevice. It is also preferred that such materials exhibits highstiffness. Opposite to the posts, the hinge (e.g. hinge 240 in FIG. 3D)are expected to be more compliant because the hinge deforms while themicromirror plate rotates. Moreover, the hinge is desired to beelectrically conducting such that the micromirror plate can be held at aparticular voltage level.

In order to achieve the defined “OFF” states in FIG. 4B and FIG. 4D,external forces (e.g. electrical fields) may required to rotate themicromirror plate. For example, an electrode 283 and circuitry may bedisposed underneath the portion of the micromirror plate being rotatedaway from the substrate. An electric field can then be applied betweenthe electrode and the portion of the micromirror plate for rotating themicromirror plate to the “OFF” state. This design, however, requiresextra electrodes and circuitry.

According to an aspect of the invention, a hinge-support with a portionthat is curved away from the substrate at the natural resting state isproposed, as shown in FIG. 5A. Referring to FIG. 5A, hinge-supportportion 250 is curved away from the substrate at its natural restingstate. And micromirror plate 210, which is attached to the curvedhinge-support, presents a finite angle with the substrate withoutexternal force (e.g. external electrical field). By adjusting thecurvature of the hinge-support portion, a desired angle between themicromirror plate and the substrate can be achieved.

The curved hinge-support can be formed in many different ways. Anexemplary method will be discussed in the following with references toFIG. 5 b and FIG. 5C. Referring to FIG. 5B, hinge-support 250 composestwo layers, layer 251 and layer 253. Layer 251 exhibits an outwardscompression strain at its deposition state (e.g. when layer 251 isdeposited on a sacrificial layer). In the preferred embodiment of theinvention, layer 251 is TiN_(x) with a preferred thickness of 80 Å.Though preferred, layer 251 can be of any suitable material as long asit exhibits an outwards compression strain. The thickness of layer 251can also be of any suitable range, such as a thickness between 10 Å to1500 Å. Layer 253 is deposited on layer 251 and exhibits an inwardstensile strain at its deposition state. In a preferred embodiment of theinvention, layer 253 is SiN_(x) with a preferred thickness of 400 Å.Though preferred, layer 253 can be of any suitable material as long asit exhibits an inwards tensile strain. The thickness of layer 253 canalso be of any suitable range, such as a thickness between 10 Å to 2000Å. PVD (physical vapor deposition or sputtering) tends to producecompressive films, especially for high melting temperature metals,whereas CVD (chemical vapor deposition) tends to produce tensile films.Therefore, in one embodiment layer 251 is a layer deposited by PVD andlayer 253 is deposited by CVD. In one specific example, layer 251 is areactively sputtered ceramic layer and layer 253 is a ceramic layerdeposited by chemical vapor deposition.

After releasing, (for example, by removing the sacrificial layer, onwhich layer 251 is deposited), layers 253 and 251 curve towards layer253, which exhibits inwards tensile strain. This curving of the twolayers is a spontaneous phenomenon and happens in the presence ofmaterial stresses. The curvature is determined upon the relativemagnitudes of the inwards tensile strain, the outwards compressionstrain and the elastic moduli. Referring to FIG. 5C, a schematic diagramshowing the curved two layers is presented therein. However, dependingupon the location of the hinge connection to the mirror plate, the orderof the layers can be reversed in order to cause curvature of the hingestructure in the opposite direction while rotating the mirror plate inthe same direction for the “OFF” state.

There is a variety of ways to construct the micromirror device describedabove. Exemplary processes will be discussed in the following withreferences to FIG. 6A through FIG. 6H. It should be appreciated by thoseskilled in the art that the exemplary processes are for demonstrationpurpose only and should not be interpreted as limitations.

Referring to FIG. 6A, substrate 280 is provided. First sacrificial layer290 is deposited on the substrate followed by the deposition ofmicromirror plate layer 300. The substrate can be a glass (e.g. 1737F,Eagle 2000), quartz, Pyrex™, sapphire. The substrate may also be asemiconductor substrate (e.g. silicon substrate) with one or moreactuation electrodes and/or control circuitry (e.g. CMOS type DRAM)formed thereon.

First sacrificial layer 290 is deposited on substrate 280. Firstsacrificial layer 290 may be any suitable material, such as amorphoussilicon, or could alternatively be a polymer or polyimide, or evenpolysilicon, silicon nitride, silicon dioxide, etc. depending upon thechoice of sacrificial materials, and the etchant selected. If the firstsacrificial layer is amorphous silicon, it can be deposited at 300-350°C. The thickness of the first sacrificial layer can be wide rangingdepending upon the micromirror size and desired title angle of themicro-micromirror, though a thickness of from 500 Å to 50,000 Å,preferably around 10,000 Å, is preferred. The first sacrificial layermay be deposited on the substrate using any suitable method, such asLPCVD or PECVD.

As an optional feature of the embodiment, anti-reflection layer 285maybe deposited on the surface of the substrate. The anti-reflectionlayer is deposited for reducing the reflection of the incident lightfrom the surface of the substrate. Alternatively, other opticalenhancing layers may be deposited on either surface of the glasssubstrate as desired.

After depositing the first sacrificial layer, a plurality of structurelayers will be deposited and patterned as appropriate. According to theinvention, a structural layer is a layer that will not be removed afterthe removal of the sacrificial layers. The first structural layerdeposited on the first sacrificial layer is micromirror plate layer 300for forming a micromirror. Because the micromirror is designated forreflecting incident light in the spectrum of interest (e.g. visiblelight spectrum), it is preferred that the micromirror plate layercomprises of one or more materials that exhibit high reflectivity(preferably 90% or higher) to the incident light. According to theembodiment of the invention, micromirror plate layer 300 is amulti-layered structure as shown in FIG. 6B. Referring to FIG. 6B, hingeplate layer 300 comprises layers 307, 305, 303 and 301. Layers 307 and301 are protection layers for protecting the interior layers (e.g.layers 303 and 305). In the preferred embodiment of the invention,layers 307 and 301 are SiO_(x) with a preferred thickness of 400 Å. Ofcourse, other suitable materials may also be employed herein. Layer 305is a light reflecting layer that comprises one or more materialsexhibiting high light reflectivity. Examples of such materials are Al,AlTi_(x) (x<0.05), AlSi_(x)Cu_(y) (x<0.05, and y<0.03) or Ag. In thepreferred embodiment of the invention, layer 305 is aluminum with athickness of 2500 Å. This aluminum layer is preferred to be deposited at150° C. or other temperatures preferably less than 400° C. Layer 303 isan enhancing layer that comprises of metal or metal alloy for enhancingthe electric and mechanical properties of the micromirror plate. Anexample of such enhancing layer is titanium with a thickness of 80 Å. Ofcourse, other suitable materials having high reflectivity to theincident light of interest may also be adopted for the micromirrorplate. In depositing the micromirror plate layer, PVD is preferably usedat 150° C. The thickness of the micromirror plate layer can be wideranging depending upon the desired mechanical (e.g. extrinsic stiffnessor strength), the size of the micromirror, desired tilt angle andelectronic (e.g. conductivity) properties of the micromirror plate andthe properties of the materials selected for forming the micromirrorplate. According to the invention, a thickness of from 500 Å to 50,000Å, preferably around 2500 Å, is preferred.

According to another embodiment of the invention, the light reflectinglayer 305 is an electro-conducting layer that comprises a materialhaving a resistivity less than 10,000 μΩ·cm. Layers 301 and 307 areinsulators with resistivities greater than 10,000 μΩ·cm. And layer 303is an electro-conducting layer with a resistivity also less than 10,000μΩ·cm.

Though the multilayered structure as shown in FIG. 6B preferablycomprises four layers, it will be appreciated by those ordinary skillsin the art that the number of the multilayered structure should not beinterpreted as a limitation. Instead, any number of layers (including asingle layer) can be employed without departing from the spirit of thepresent invention.

Micromirror plate layer 300 is then patterned into a desired shape, asshown in FIG. 6C. The micromirror can be of any shape as desired. Thepatterning of the micromirror can be achieved using standard photoresistpatterning followed by etching using, for example CF4, C12, or othersuitable etchant depending upon the specific material of the micromirrorplate layer.

After the formation of the micromirror plate, further structural layersare deposited and patterned. Specifically, a plurality of layers of thehinge structure will be deposited and patterned for forming the bingestructure. Referring to FIG. 6D, before depositing further structurallayers, second sacrificial layer 310 is deposited on top of themicromirror plate 300 and first sacrificial layer 290. Secondsacrificial layer 310 may comprise amorphous silicon, or couldalternatively comprise one or more of the various materials mentionedabove in reference to first sacrificial layer 290. First and secondsacrificial layers need not be the same, though are the same in thepreferred embodiment so that, in the future, the etching process forremoving these sacrificial layers can be simplified. Similar to thefirst sacrificial layer, second sacrificial layer 310 may be depositedusing any suitable method, such as LPCVD, PECVD or sputtering. If thesecond sacrificial layer comprises amorphous silicon, the layer can bedeposited at 350° C. The thickness of the second sacrificial layer canbe on the order of 9000 Å, but may be adjusted to any reasonablethickness, such as between 2000 Å and 20,000 Å depending upon thedesired distance (in the direction perpendicular to the micromirrorplate and the substrate) between the micromirror plate and the hinge. Itis preferred that the hinge and mirror plate be separated by a gap afterrelease of at least 0.5 um (this can be at least 1 um or even 2 um ormore if desired). Second sacrificial layer 310 may also fill in thetrenches left from the patterning of the micromirror plate.

In the preferred embodiment of the invention, the micromirror platelayer comprises an aluminum layer (e.g. layer 305 in FIG. 6B), and thesecond sacrificial layer is amorphous silicon. This design, however, cancause defects in the micromirror device due to the diffusion of thealuminum and silicon at the edges of the micromirror plate, wherein thealuminum is exposed to the silicon. To solve this problem, a diffusionbarrier layer (not shown) maybe deposited on the patterned micromirrorplate before depositing the second sacrificial silicon layer such thatthe aluminum layer can be isolated from the silicon sacrificial layer.Then the protection layer is patterned according to the shape of themicromirror plate. After the patterning, segments of the protectionlayer (e.g. segment 211 in FIG. 6C) cover the edges of the micromirrorplate for isolating the aluminum and the silicon sacrificial layer.

The deposited second sacrificial layer is patterned afterwards forforming two deep-via areas 320 and shallow via area 330 using standardlithography technique followed by etching, as shown in FIG. 6E. Theetching step may be performed using Cl₂, BCl₃, or other suitable etchantdepending upon the specific material(s) of the second sacrificial layer.The distance across the two deep-via areas 320 depends upon the lengthof the defined diagonal of the micromirror plate. In an embodiment ofthe invention, the distance across the two deep-via areas after thepatterning is preferably around 10 μm, but can be any suitable distanceas desired. In order to form shallow-via area 330, an etching step usingCF₄ or other suitable etchant may be executed. The shallow-via area,which can be of any suitable size, is preferably on the order of 2.2 μmon a side.

Hinges and Hinge Materials

Referring to FIG. 6F, hinge-support layers 340 and 350 are deposited onthe patterned second sacrificial layer 310. Because the hinge-supportlayers (layers 340 and 350) are designated for holding the hinge (e.g.240 in FIG. 3D) and the micromirror plate (e.g. 210 in FIG. 3C) attachedtherewith such that the micromirror plate can pivot along the hinge, itis desired that the hinge support layers comprise of materials having alarge elastic modulus. According to an embodiment of the invention,layer 340 comprises a 400 Å thickness of TiN_(x) (although it maycomprise both TiN_(x) with any suitable thickness such as between 100 Åand 2000 Å deposited by PVD, and a 3500 Å thickness of SiN_(x)—althoughthe thickness of the SiN_(x) layer may be any suitable thickness such asbetween 2000 Å and 10,000 Å) layer 350 deposited by PECVD. Of course,other suitable materials and methods of deposition may be used (e.g.methods, such as LPCVD or sputtering). The TiN_(x) layer is notnecessary for the invention, but provides a conductive contact surfacebetween the micromirror and the hinge support structure in order to, atleast, reduce charge-induced stiction. According to the embodiment ofthe invention, layers 340 and 350 are deposited such that an inwardscompression strain and outwards tensile strain are inherently presentedfor forming a curved hinge-support (e.g. 250 in FIG. 5A), as shown inFIG. 5C. Alternatively, the TiN_(x) and SiNx layers can also bedeposited such that the intrinsic stress is as low as possible,preferably lower than 250 MPa for forming a flat hinge-support. Ineither case, the SiN_(x) layer can be deposited at 400° C.

After the deposition, layers 340 and 350 are patterned into a desiredconfiguration (e.g. hinge support 275 in FIG. 3D), as shown in FIG. 6G.Posts 260 can take any desired forms, one of which is shown in FIG. 3D.Alternatively, each of the two posts may be formed as a diamond, such asposts 251 in FIG. 3F. The mirror stops, such as the mirror stops (e.g.mirror stops 270 in FIG. 3D) corresponding to the “ON” state and/ormirror stops (not shown) corresponding to the “OFF” state can also beconfigured. An etching step using one or more proper etchants is thenperformed afterwards. In particular, the layers can be etched with achlorine chemistry or a fluorine chemistry where the etchant is aperfluorocarbon or hydrofluorocarbon (or SF₆) that is energized so as toselectively etch the hinge support layers both chemically and physically(e.g. a plasma/RIE etch with CF₄, CHF₃, C₃F₈, CH₂F₂, C₂F₆, SF₆, etc. ormore likely combinations of the above or with additional gases, such asCF₄/H₂, SF₆/Cl₂, or gases using more than one etching species such asCF₂Cl₂, all possibly with one or more optional inert diluents).Different etchants may, of course, be employed for etching each hingesupport layer (e.g. chlorine chemistry for a metal layer, hydrocarbon orfluorocarbon (or SF₆) plasma for silicon or silicon compound layers,etc.). Alternatively, the etching step can be performed after depositionof each hinge support layer. For example, layer 340 can be etched andpatterned after the deposition of layer 340 and before the deposition oflayer 350.

After etching layers 340 and 350, two posts 260 and a contact area 330are formed. The bottom segment of contact area 330 is removed by etchingand the part of the micromirror plate underneath the contact area isthus exposed. The exposed part of micromirror 210 will be used to forman electric-contact to an external electric source. The sidewalls (e.g.335) of contact area 330 are left with residues of layers 340 and 350after etching. The residue 335 has a slope measured by angle, θ,approximately 75 degrees, but may vary between 0 and 89 degrees. Theresidue on the sidewalls helps to enhance the mechanical and electricalproperties of the hinge that will be formed afterwards. Each of the twoposts 260 on either side of the mirror can form a continuous elementwith the posts corresponding to the adjacent micromirror in an array asshown in FIG. 2.

After the completion of patterning and etching of layers 340 and 350,hinge layer 360 is deposited and then patterned as shown in FIG. 6H.Because the hinge provides a rotation axis for the micromirror plate, itis natural to expect that the hinge layer comprises a material that isnot susceptible to plastic deformation (e.g. fatigue, creep, anddislocation motion). Furthermore, when the hinge layer is also used aselectric contact for the micromirror plate, it is desired that thematerial of the hinge layer is electrically conductive, or at least oneof the layers has some electrical conductivity if a multi-layer hinge isprovided.

After deposition, the hinge layer(s) is then patterned as desired with asuitable etchant. Similar to the hinge layers (layers 340 and 350), thehinge layer can be etched with a chlorine chemistry or a fluorinechemistry where the etchant is a perfluorocarbon or hydrofluorocarbon(or SF₆) that is energized so as to selectively etch the hinge layersboth chemically and physically (e.g. a plasma/RIE etch with CF₄, CHF₃,C₃F₈, CH₂F₂, C₂F₆, SF₆, etc. or more likely combinations of the above orwith additional gases, such as CF₄/H₂, SF₆/Cl₂, or gases using more thanone etching species such as CF₂Cl₂, all possibly with one or moreoptional inert diluents). Different etchants may, of course, be employedfor etching different hinge layers

In order to release the micromirror plate for pivoting along the hinge,the sacrificial layers (e.g. layers 290 and 310) are removed by etchingas discussed below. A cross-sectional view of the released micromirrordevice is presented in FIG. 8.

In the above described exemplary fabrication process, the processes forforming the hinge support (e.g. processes described in FIG. 6A to FIG.6G) and the process for forming the hinge (e.g. process described inFIG. 6H) are performed consecutively. In particular, the patterning andetching of the hinge support is followed by the deposition, patterningand etching of the hinge. The hinge and the hinge support can be formedsimultaneously according to another embodiment of the invention, whichwill be described in the following with references to FIG. 7A and FIG.7B.

Referring to FIG. 7A, the deposited hinge layers 340 and 350 for thehinge support (e.g. 275 in FIG. 3D) are first patterned and etchedaccording to the desired configuration of the hinge. After etching,window 370 corresponding to the future location of the hinge (e.g. hinge240 in FIG. 3D) is thus formed thereby. Window 370 is disposed parallelto but offset from a diagonal of the micromirror plate. The window isetched down to the top surface of the second sacrificial layer (e.g. 310in FIG. 6D) and/or micromirror plate such that the bottom of the windowexposes a part of the micromirror plate.

Following the completion of the patterning, hinge layer 360 is depositedon the patterned hinge support layer (e.g. 350) and fills window 370.After deposition, layer 340, 350 and 360 are then patterned and etchedsimultaneously. In a preferred embodiment of the invention, layers 340and 350 are patterned and etched simultaneously using the same methodthat is described in FIG. 6G. After patterning and etching of layers 340and 350, the sacrificial layers are removed by etching for releasing themicromirror device.

As mentioned above, the flexible part of the MEMS device can be formedof a transition metal nitride which is resistant to attack by thespontaneous gas phase chemical etchant used in the final release. Thetransition metal nitride layer is preferably formed by sputtering atransition metal target (e.g. a single transition metal, more than onetransition metal such as an alloy of two or more transition metals, or atransition metal compound (e.g. transition metal aluminide or preferablysilicide) in nitrogen gas. Though the target could be a combination ofmore than one transition metal (or two transition metals in alloy form),in one embodiment it is preferred that the target comprise a singletransition metal, or one (or more) transition metals and one or moremetalloids (and, perhaps, minute quantities of impurities such as O, H,other transition metals, metalloids, etc., which are often present invarious sputtering methods). In one embodiment, the target comprises atleast one transition metal and at least one metalloid. In anotherembodiment, the target comprises a single transition metal without anyother metals except perhaps as impurities or in trace amounts. In such acase, it is preferred that the transition metal of the target make up90% or more of the target, preferably 98% or more. And, though nitrogenand argon are the preferred gases for reactive sputtering in the presentinvention (e.g. 20% N2, 80% Ar), small amounts of oxygen or hydrogen (orcompounds thereof such as a transition metal oxide in small amounts) canbe present in the layer or structure being formed (the oxygen and/orhydrogen in the layer coming from target “impurities” or from thesputtering gas.

The sputtering or PVD (physical vapor deposition) can be performed inany of a number of known PVD systems, including dc glow-dischargesputtering systems, rf glow discharge sputtering systems, and magnetronsputtering systems. Commercially available examples include the Varia(3000 series) sputtering system, the Applied Materials Endura VHP PVDsystem, the Applied Materials Centura HP PVD system, and the MRC EclipseSputtering system. Other systems and methods are disclosed in theHandbook of Physical Vapor Deposition, D. M. Mattox, 1998, incorporatedherein by reference. The sputtering target can be any suitable target,such as one supplied by Cerac, Honeywell or Praxair.

The transition metals are those elements in the periodic table incolumns 3 to 12 (1B to 8B), namely columns beginning with Sc, Ti, V, Cr,Mn, Fe, Co, Ni, Cu and Zn. Preferred are those elements in columns 3B,4B, 5B, 6B and 7B—however late transition metals in columns 8B, 1B and2B are also possible in the present invention, though preferably inconjunction with an early transition metal. In one embodiment of theinvention, a single transition metal is sputtered from a target in anitrogen atmosphere to form a (single) transition metal nitride. It isalso within the invention to provide a target with more than onetransition metals (or a plurality of targets with different transitionmetals). In one embodiment of the invention, the target comprises atleast one late transition metal—and single or multiple early transitionmetals that each form nitrides when sputtered. The late transition metaltarget can also comprise one or more early transition metals and/or oneor more metalloids (B, Si, Ge, As, Sb)—each forming nitrides duringsputtering. It is also possible to use only metalloids (a singlemetalloid or more than one metalloid in the target), though having atleast one transition metal is preferred in the present invention.Processing parameters can be optimized to increase amorphousness of thedeposited film.

If a plurality of metals or metalloids is present in the MEMS structure,each need not be formed as a compound with nitrogen. It is within theinvention that one transition metal or metalloid is in nitride form, andan additional metal or metalloid is present in element form. Forexample, a single transition metal nitride can be present in the MEMSstructure along with an additional metal or metalloid in elemental form.Likewise, a metalloid nitride can be present in the MEMS structure alongwith an additional metal or metalloid in compound or elemental form. Ina specific embodiment, the MEMS structure comprises a transition metalnitride and a metalloid nitride (e.g. silicon nitride) and the etchantis a noble gas fluoride. In another embodiment, the MEMS structurecomprises a transition metal nitride or a transition metal oxynitridewith optional minor amounts of boron, carbon or phosphorous. Preferredearly transition metal nitrides (including early transition metalsilicon nitrides, oxynitrides, silicon oxynitrides, carbonitrides etc.)are those from columns 3b (Sc, Y, Lu, Lr), 4b (Ti, Zr, Hf, Rf), 5b (V,Nb, Ta, Db), 6b (Cr, Mo, W, Sg) and 7b (Mn, Tc, Re, Bh) of the periodictable. However, preferred are early transition metals in columns 4b to6b, in particular tungsten, titanium, zirconium, hafnium, niobium,tantalum, vanadium and chromium.

Si and B are preferred metalloids, though any of the metalloids can beused in the present invention. Ti, V, Zr, Ta and W are preferred earlytransition metals, though any of the early transition metals can be usedin the present invention in accordance with the above. Some specificexamples within the present invention include tantalum nitride, tantalumsilicon nitride, tantalum oxynitride, tantalum silicon oxynitride,vanadium nitride, vanadium oxynitride, titanium nitride, titaniumsilicon nitride, titanium silicon oxynitride, titanium boronitride,zirconium nitride, tungsten silicon nitride, tungsten nitride, tungstensilicon oxynitride, tungsten oxynitride, tungsten silicon carbonitride,molybdenum silicon nitride, molybdenum silicon oxynitride, tungstenboronitride, indium nitride, hafnium nitride, zirconium silicon nitride,vanadium silicon nitride, vanadium boronitride, tantalum boronitride,scandium boronitride, scandium nitride, scandium silicon nitride andmolybdenum boronitride. Preferred are binary (nitrides) or ternarynitrides of titanium, tantalum and tungsten (e.g. silicon nitrides,silicon oxynitrides, oxynitrides). These are but a few examples that canbe used for the MEMS structure (particularly the flexible portion of theMEMS device) as set forth herein.

Silicon can be added to the target so that the film formed resembles alate transition metal+SiNx (in one embodiment of the invention, twoearly transition metals and silicon are part of a target, whereas inanother embodiment of the invention, one or more late transition metalsand silicon are present in the target). Some of these types of films aredisclosed in U.S. provision application Ser. No. 60/228,007 to Reid etal. filed Aug. 23, 2000, incorporated herein by reference. Also, nearmetalloids such as phosphorous and/or carbon can be added to thetransition metal target so as to form transition metal—phosphonitridesand/or transition metal—carbonitrides. Oxygen is preferably not presentin the sputtering atmosphere if electrically conductive films aredesired—however, some transition metals form electrically conductivecompounds with oxygen, e.g. Ru and In (which form RuO2 and In2O3).

Many variations from the above-described examples are possible. Forexample, in place of sputtering the films as described above, it is alsopossible to deposit the films by chemical vapor deposition (e.g. PECVDor LPCVD). Also, though electrically conductive films are preferred inthe present invention, electrically insulating films are also with thescope of the invention. And, electrically insulating films (e.g. manymetal nitrides) can be formed with elemental metals or metalloids toimprove conductivity if conductivity is desired.

In a preferred embodiment of the invention, the hinge materials aboveare used in a process for releasing the MEMS devices in a spontaneousvapor phase chemical etchant, such as a noble metal halide or aninterhalogen. The release etching utilizes an etchant gas capable ofspontaneous chemical etching of the sacrificial material, preferablyisotropic etching that chemically (and not physically) removes thesacrificial material. Such chemical etching and apparatus for performingsuch chemical etching are disclosed in U.S. patent application Ser. No.09/427,841 to Patel et al. filed Oct. 26, 1999, and in U.S. patentapplication Ser. No. 09/649,569 to Patel at al. filed Aug. 28, 2000, thesubject matter of each being incorporated herein by reference. Preferredetchants for the release etch are gas phase fluoride etchants that,except for the optional application of temperature, are not energized.Examples include HF gas, noble gas halides such as xenon difluoride,xenon tetrafluoride and interhalogens such as IF₅, BrCl₃, BrF₃, IF₇ andClF₃. The release etch may comprise additional gas components such as N₂or an inert gas (Ar, Xe, He, etc.). In this way, the remainingsacrificial material is removed and the micromechanical structure isreleased. In one aspect of such an embodiment, XeF₂ is provided in anetching chamber with diluents (e.g. N₂ and He). The concentration ofXeF₂ is preferably 8 Torr, although the concentration can be varied from1 Torr to 30 Torr or higher. This non-plasma etch is employed forpreferably 900 seconds, although the time can vary from 60 to 5000seconds, depending on temperature, etchant concentration, pressure,quantity of sacrificial material to be removed, or other factors. Theetch rate may be held constant at 18 Å/s/Torr, although the etch ratemay vary from 1 Å/s/Torr to 100 Å/s/Torr. Each step of the releaseprocess can be performed at room temperature.

In addition to the above etchants and etching methods mentioned for usein either the final release or in an intermediate etching step, thereare others that may also be used by themselves or in combination. Someof these include wet etches, such as ACT, KOH, TMAH, HF (liquid); oxygenplasma, SCCO₂, or super critical CO₂ (the use of super critical CO₂ asan etchant is described in U.S. patent application Ser. No. 10/167,272,which is incorporated herein by reference). Of course, the etchants andmethods selected should be matched to the sacrificial materials beingremoved and the desired materials being left behind. However, preferredare the spontaneous vapor phase chemical etchants that etchisotropically in the absence of a plasma—such as those noted above.

It will be appreciated by those of skill in the art that a new anduseful spatial light modulator has been described herein. In view of themany possible embodiments to which the principles of this invention maybe applied, however, it should be recognized that the embodimentsdescribed herein with respect to the drawing figures are meant to beillustrative only and should not be taken as limiting the scope ofinvention. For example, those of skill in the art will recognize thatthe illustrated embodiments can be modified in arrangement and detailwithout departing from the spirit of the invention. In particular, eachof the layers of the structure layers, such as micromirror plate layer300 (which may further comprises layers 301, 303, 305 and 307 as shownin FIG. 6B), hinge support layers 340 and 350, and hinge layer 360 maycomprise one or more of a number of suitable materials that are eitherelectro-conducting or electro-insulating, as long as at least one of thelayers is electro-conducting and provides electro-contact to themicromirror. Also, though PVD and CVD are referred to above, other thinfilm deposition methods could be used for depositing the layers,including spin-on, sputtering, anodization, oxidation, electroplatingand evaporation. Therefore, the invention as described hereincontemplates all such embodiments as may come within the scope of thefollowing claims and equivalents thereof.

1. A method for making a microelectromechanical device, the methodcomprising: depositing a sacrificial material on a substrate; forming anarray of MEMS elements comprised of plates and hinges, wherein thehinges of the MEMS elements comprise an early transition metal (groups3b-7b of the periodic table) nitride; and releasing the MEMS elements byremoving the sacrificial material in a spontaneous gas phase chemicaletchant selected from interhalogens and noble gas halides, wherein theearly transition metal nitride is exposed to the etchant during removalof the sacrificial material but remains after the MEMS elements arereleased.
 2. The method of claim 1, wherein the hinges are titaniumnitride or titanium silicon nitride and the etchant is xenon difluoride.3. The method of claim 1, wherein the hinges are a laminate comprising alayer of silicon nitride and a layer of an early transition metalnitride.
 4. The method of claim 1, wherein the hinges comprise both anearly transition metal nitride and a late transition metal.
 5. Themethod of claim 1, wherein the hinges comprise a material selected fromNbN, VN, HfN, ZrN and YN.
 6. The method of claim 1, wherein the hingeshave a length to width ratio of 2:1 to 40:1.
 7. The method of claim 1,wherein the hinges have a length to thickness ratio of from 50:1 to200:1.
 8. The method of claim 1, wherein the length of each hinge isless than 20 micrometers.
 9. The method of claim 1, wherein the width ofeach hinge is greater than 0.1 micrometers and less than 2 micrometers.10. The method of claim 1, further comprising packaging the MEMS elementarray and placing the packaged array in a projection display apparatus.11. The method of claim 1, wherein the hinges are electricallyconductive.
 12. The method of claim 1, wherein the hinges aremulti-layer hinges.
 13. The method of claim 12, wherein the hingescomprise a layer of titanium silicon nitride and a layer of titaniumnitride.
 14. The method of claim 12, wherein a layer of the multi-layerhinges comprises titanium.
 15. The method of claim 12, wherein a layerof the multilayer hinges comprise tungsten.
 16. The method of claim 1,wherein the etchant is an interhalogen.
 17. The method of claim 16,wherein the etchant is BrF3 or BrCl3.
 18. The method of claim 1, whereinthe etchant is a noble gas halide.
 19. The method of claim 18, whereinthe etchant is xenon difluoride.
 20. The method of claim 18, wherein thesacrificial material comprises amorphous silicon.
 21. The method ofclaim 18, wherein the sacrificial material comprises an early transitionmetal.
 22. The method of claim 1, wherein the vertical depth of eachhinge is from 30 to 1000 Angstroms.
 23. The method of claim 22, whereinthe vertical depth of each hinge is from 300 to 600 Angstroms.
 24. Themethod of claim 1, wherein the hinges are formed by reactivelysputtering a target in a nitrogen gas.
 25. The method of claim 24,wherein the hinges are formed by reactively sputtering an earlytransition metal target in a nitrogen or nitrogen/oxygen gas.
 26. Themethod of claim 24, wherein the hinges are formed by reactivelysputtering an early transition metal silicide target in a nitrogen ornitrogen/oxygen gas.
 27. The method of claim 1, wherein the step offorming the array of MEMS elements comprises: depositing the sacrificialmaterial in a first layer; depositing further sacrificial material in asecond layer; wherein plates are deposited and patterned on one of thesacrificial layers and hinges are deposited and patterned on the otherof the sacrificial layers.
 28. The method of claim 27, wherein the firstand second sacrificial layers comprise the same material.
 29. The methodof claim 27, wherein the forming of the array of MEMS elementscomprises: forming the plates on the deposited sacrificial material inthe first layer and; forming the hinges on said further sacrificialmaterial in the second layer.
 30. The method of claim 29, wherein thesubstrate is a substrate transmissive to visible light.
 31. The methodof claim 27, wherein the forming the array of MEMS elements comprises:forming the hinges on the deposited sacrificial material in first layerand; forming the plates on said further sacrificial material in thesecond layer.
 32. The method of claim 31, wherein the substrate is asemiconductor substrate.
 33. The method of claim 1, wherein the MEMSelements are operable in binary mode and are rotatable from anon-deflected state to an ON state, the ON state being at least 10degrees from the non-deflected state.
 34. The method of claim 33,wherein the ON state is at least 12 degrees from the non-deflectedstate.
 35. The method of claim 34, wherein the ON state is at least 14degrees from the non-deflected state.
 36. The method of claim 1, hereinthe early transition metal of the early transition metal nitride isselected from titanium, tantalum, chromium, molybdenum and tungsten. 37.The method of claim 36, wherein the plates comprise a reflectivealuminum layer.
 38. The method of claim 36, wherein the plates comprisea reflective silver layer.
 39. The method of claim 36, wherein the earlytransition metal is tungsten.
 40. The method of claim 39, wherein thehinges comprise tungsten silicon nitride.
 41. The method of claim 39,wherein the hinges comprise tungsten titanium nitride.
 42. The method ofclaim 39, wherein the hinges comprise tungsten oxynitride or tungstencarbonitride.
 43. The method of claim 36, wherein the early transitionmetal is molybdenum.
 44. The method of claim 43, wherein the hingescomprise molybdenum silicon nitride.
 45. The method of claim 36, whereinthe early transition metal is tantalum.
 46. The method of claim 45,wherein the hinges comprise tantalum oxynitride.
 47. The method of claim45, wherein the hinges comprise tantalum nitride.
 48. The method ofclaim 45, wherein the hinges comprises tantalum silicon nitride ortantalum silicon oxynitride.
 49. The method of claim 45, wherein thehinges comprise tantalum titanium nitride.
 50. The method of claim 45,wherein the hinges comprises tantalum titanium silicon oxynitride. 51.The method of claim 36, wherein the hinges further comprise siliconnitride.
 52. The method of claim 51, wherein the hinges further comprisea late transition metal.
 53. The method of claim 36, wherein the earlytransition metal is titanium.
 54. The method of claim 53, wherein thehinges comprise titanium silicon nitride.
 55. The method of claim 53,wherein the hinges comprise titanium nitride.
 56. The method of claim53, wherein the hinges comprise titanium oxynitride.
 57. The method ofclaim 56, wherein the hinges comprise titanium silicon oxynitride. 58.The method of claim 36, wherein the early transition metal is chromium.59. The method of claim 58, wherein the hinges comprise chromiumnitride.
 60. The method of claim 59, wherein the hinges comprisechromium oxynitride.
 61. A method for making a micromirror array for aprojection display, comprising: depositing a sacrificial material on asubstrate; forming an array of micromirrors comprised of mirror platesand hinges, wherein the hinges of the micromirrors comprise an earlytransition metal (groups 3-7 of the periodic table) nitride; andreleasing the micromirrors by removing the sacrificial material in aspontaneous gas phase chemical etchant selected from interhalogens andnoble gas halides, wherein the early transition metal nitride is exposedto the etchant during removal of the sacrificial material but remainsafter the micromirrors are released.
 62. A method of making amicromirror array device, the method comprising: deposition asacrificial material on a substrate; forming an array of micromirrorscomprised of mirror plates and hinges, wherein the hinges compriseTiN_(x); and releasing the micromirrors by removing the sacrificialmaterial in a spontaneous gas phase etchant comprising gas phase xenondifluoride, wherein the TiN_(x) is exposed to the etchant during removalof the sacrificial material but remains after the micromirrors beingreleased.
 63. The method of claim 62, wherein the hinge furthercomprises silicon nitride.
 64. The method of claim 62, wherein thesubstrate is a light transmissive substrate.
 65. The method of claim 62,wherein the step of forming an array of micromirrors further comprises:depositing the sacrificial material in a first layer; depositing thesacrificial material in a second layer; wherein the plates are depositedand patterned on one of the first and second layers; and wherein thehinges are deposited and patterned on the other one of the first andsecond layers.
 66. The method of claim 65, wherein the sacrificialmaterial on the first and second layer comprise the same material. 67.The method of claim 65, wherein the hinges are deposited and patternedbefore the plates.
 68. The method of claim 65, wherein the plates aredeposited and patterned before the hinges.